In recent years, mobile wireless communications have become increasingly popular. Initial implementations of mobile wireless communications, for example in the form of cellular telephone networks, supported circuit switched voice communication services. Today wireless carriers also offer packet data communication services to their mobile customers.
Prepaid communications services, in which a customer or subscriber prepays for usage of a communications system, have become increasingly popular. Such services now encompass an array of mobile wireless communications. In an example of a prepaid wireless service, the customer may purchase blocks of time for making voice telephone calls via a cellular telephone network. Upon connecting to the wireless communications network, the customer account is authorized and authenticated, and the network allows a call to proceed. The network monitors the customer's usage time and decrements from the customer's account. If the account becomes depleted, the system can either prompt the customer to purchase more time, or the system can terminate the call. Prepaid wireless communications system enable the customer to budget an amount of airtime that will be used during a certain period of time, and to insure that the budget will not be exceeded unless the customer purchases more airtime. The wireless service provider likes this type of service, because the carrier receives payment in advance and need not run the risk that the customer will default on a bill, as sometimes happens with postpay type billing services.
Service providers have extended their prepaid offerings to encompass various wireless data services. For example, commonly assigned U.S. patent application Ser. No. 10/247,034 to Varsha Clare et al. discloses a “Method and System for Processing Prepaid Wireless Data Communications.” As disclosed there, a receiving node, such as a packet data serving node (PDSN), handles packet data calls and interacts with an administration system, including an authentication, authorization and accounting (AAA) server and a prepaid server platform. Upon receiving a packet data call, the PDSN accesses the AAA server to obtain call access authorization. For a prepaid customer, with the authorization, the PDSN also receives a prepaid volume record indicating an amount of prepaid units available for use by the customer and processing instructions, from the server platform for the prepaid service. The PDSN then enables the wireless data call to proceed on the network, while monitoring the call and decrementing the available prepaid units from the prepaid volume record associated with the customer. If the available prepaid units reach a predetermined level, as indicated in the processing instructions, the PDSN notifies the prepaid service server that the predetermined level has been reached. The server system can respond either with an updated available balance, which enables the PDSN to allow the call to continue, or with instructions to the PDSN to terminate the call.
As another example, US published patent application no. 2004/0106393 relates to “Methods, systems and program products for supporting prepaid service within a communication network,” specifically for a prepaid packet data communication service. A prepaid client, for example in a foreign agent (FA) PDSN or in a home agent (HA), sends a resource request for prepaid resources through the network to a prepaid server. In response, the prepaid server transmits a resource response that specifies a quota of prepaid resources. The quota is no greater than the prepaid account balance of the subscriber. The resource response also includes a resource usage threshold at which the prepaid client will provide notification and will update the account to reflect a portion of the prepaid account balance that has been consumed.
Hence, a modern prepaid packet data (PPD) service allows the subscriber to pay for packet data service prior to usage. In an actual deployment, when a subscriber establishes a prepaid account with the wireless service provider, for packet data service, appropriate provisioning is made at the carrier's Authentication, Authorization and Accounting (AAA) and prepaid server platforms, to allow the subscriber to receive prepaid data service. The AAA server acts as a proxy for the prepaid user's Remote Authentication Dial-User Service (RADIUS) messages, except for accounting messages. The AAA server proxies the RADIUS messages to the provisioned prepaid service platform.
The Packet Data Serving Node (PDSN) and the Home Agent (HA) act as TIA-835-C prepaid clients. TIA-835-C is a standard for by 3GPP2 for a cdma2000 Wireless IP Network. In relevant part, that standard specifies a prepaid packet data service. The prepaid service platform acts as a TIA-835-C prepaid server (PPS). When the subscriber initiates a prepaid call, the AAA server proxies the RADIUS Access-Request to the prepaid service platform. The prepaid service platform checks the subscriber's balance, and prepaid and session termination capabilities of the serving PDSN and the customer's HA, and grants either the PDSN for SIP sessions or the PDSN or the HA for MIP sessions prepaid client (PPC) duties by providing a quota to the node serving as the PPC for the particular call.
The PPC carries out quota replenishment after threshold expiry using RADIUS online Access-Requests, which contain the amount of duration/volume used for that session. The PPC will release resources when the quota is not replenished and runs out, essentially ending the data session. When the subscriber ends a packet data session or the PPC is remotely instructed to tear down the session (by the prepaid platform), the PPC sends the information regarding the duration/volume used during the session, via the AAA server, to the prepaid platform.
The deployment using this standard-based technology supports Mobile IP (MIP). With the MIP service, the assigned IP address does not change as the mobile station changes its point of attachment to the network (e.g. by roaming across a PDSN service boundary). Although the address may be dynamically assigned at log-in, the IP address remains assigned to the particular mobile station until that station logs-off, is inactive for longer than some set period, or the data session is otherwise terminated. MIP provides routing of packets between PDSNs, to effectively enable roaming between service areas of different PDSNs.
However, problems arise in determining the duration of a communication session for prepaid accounting treatment, when the service uses MIP and the HA acts as the PPC. Many different events may cause termination of a MIP session at the HA and cause the HA to remove the MIP binding associated with the user. Some of the common scenarios that may cause a MIP session for a particular user to end at the HA include:                1. The mobile device deregisters by sending a MIP registration with a lifetime value of zero;        2. The HA MIP binding for the user expires because the mobile device failed to send a new MIP registration request within the lifetime;        3. A MIP Registration Revocation for the user was received by the HA;        4. The HA receives a RADIUS Disconnect Request message due to resource management; and        5. For prepaid users, the MIP session may be discontinued by the HA in the event that there are no more funds available.        
Prepaid accounting, for at least some data sessions, is based on duration of the session or logical data connection. Many customers prefer duration based accounting because it is far easier to understand than accounting based on number of packets or bytes of data. The different types of MIP session termination, however, cause sessions to end at different times (upon occurrence of different events), that the existing systems have not recognized. TIA-835-C is a 3GPP2 standard that specifies the PrePaid Packet Data Service for the cdma2000 Wireless IP Network. While the standard allows the Home Agent to charge based on time for a MIP session, it does not explicitly define the end time for various circumstances. As a result, the accuracy of duration-based accounting varies depending on the type of termination.
Hence, a need exists for a technique and equipment to provide prepaid accounting for packet data communication sessions, which can provide accurate accounting for duration including for sessions that terminate due to different events, e.g. to facilitate accurate duration based accounting for MIP sessions terminated in different ways.